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Biomedical subjects

A S Larsen

Publications and source records attributed to A S Larsen.

6 recordsLinked to original sources
PubMed1992

Correlated responses in lines of chickens divergently selected for fifty-six-day body weight. 2. Organ growth, deoxyribonucleic acid, ribonucleic acid, and protein content.

Growth of organs relative to body weight and cellular protein, RNA, DNA, and cell unit size of breast muscle, liver, and small intestinal tissue were measured in females from four lines of chickens. Two lines had undergone 32 generations of divergent selection for 56-day body weight, and the other two lines were derived by sampling the first two lines at Generation 28 and relaxing selection for the next five generations. The diet used in the present experiment was the same diet under which selection was practiced (20% crude protein and 2,685 kcal of ME/kg). Comparisons at common chronological ages and a common body weight revealed that supply organ weights, especially that of the small intestine, were associated with subsequent growth of demand organs. Although the upper gastrointestinal tract was also important in this respect, it was more susceptible to influences such as feed intake. Selection for juvenile body weight resulted in correlated changes in cell size of breast muscle but not liver and small intestine. Muscle increased posthatch as cells underwent hypertrophy but liver and small intestine grew chiefly by hyperplasia.

Animals↗
PubMed1992

Correlated responses in lines of chickens divergently selected for fifty-six-day body weight. 3. Digestive enzymes.

Levels of amylase, trypsin, chymotrypsin, and lipase in the pancreas and small intestinal chyme were measured in females from four lines of chickens. Two of the lines had undergone 32 generations of divergent selection for 56-day body weight, and in the other two lines selection for high or low weight had been relaxed for 5 generations. The diet used in the present experiment was that under which selection had been practiced (20% crude protein and 2,685 kcal of ME/kg). Comparisons between divergently selected lines at common ages revealed higher enzyme levels for high- than low-weight lines. When comparisons were made at a common body weight (80 +/- 5 g) there were no differences between lines. These results suggested that correlated responses in feed intake were mediating the regulation of digestive enzyme levels in the pancreas and in intestinal chyme of growth-selected lines of chickens. Chicks from high-weight lines had elevated enzyme levels after a mild feed restriction compared with those provided ad libitum access to feed. It was hypothesized that hyperphagia associated with the high-weight lines in combination with a mild feed restriction and the associated meal feeding stimulated synthesis and secretion of digestive enzymes.

Age Factors↗
PubMed1987

A tissue-specific transcriptional enhancer is found in the body of the HLA-DR alpha gene.

We mapped cis-acting regulatory elements in the HLA-DR alpha gene, which encodes the monomorphic subunit of the HLA-DR heterodimer. Genomic fragments of HLA-DR alpha were placed 5' or 3' to the chloramphenicol acetyltransferase reporter gene, the transcription of which was initiated from the Herpes simplex thymidine kinase promoter. In transient expression assays, fragments from the body of the HLA-DR alpha gene were able to increase chloramphenicol acetyltransferase activity in a position-, orientation-, and promoter-independent yet tissue-specific fashion. These HLA-DR alpha cis-acting regulatory elements contain previously identified DNase I-hypersensitive sites and DNA sequences homologous to those found in other eukaryotic transcriptional enhancers.

Acetyltransferases↗
PubMed1987

Chromatin structure of the HLA-DR alpha gene in different functional states of major histocompatibility complex class II gene expression.

We utilized DNase I hypersensitivity mapping to study chromatin structure within the HLA-DR alpha gene. We found a single DNase I-hypersensitive site coinciding with the HLA-DR alpha gene promoter in all cells studied. Moreover, in cells that constitutively express HLA-DR, two additional DNase I-hypersensitive sites were observed. These lie within the first intron of the HLA-DR alpha gene and encompass DNA sequences that share homologies with regulatory loci of the immunoglobulin and immune response genes, as well as with core enhancer consensus sequences.

Base Sequence↗